Evidence of large-scale and room-temperature stair-stepped quantum spin Hall states in Bi4Br4

Abstract

Topological insulators host exotic quantum phenomena such as the quantum spin Hall (QSH) effect, which enables dissipationless one-dimensional edge conduction. Realizing such states at room temperature and on a macroscopic scale is essential for energy-efficient electronics and quantum technologies, yet remains a fundamental challenge due to material limitations. Here, using microwave impedance microscopy, we directly visualize robust conductive channels persisting up to 300 K in α-Bi4Br4 nanowires. Their stability and scalability are likely enabled by a “stair-stepped” stacking configuration on the side facets, a multilayer geometry in which QSH edge states from individual layers remain spatially decoupled. This configuration circumvents the stringent alignment and layer-number constraints of previous proposals, allowing robust stair-stepped QSH (SS-QSH) conduction in structures several micrometers long and hundreds of nanometers high. Magnetic-field- and temperature-dependent measurements are consistent with the topological nature of these conductive channels, as further supported by our theoretical analysis. Crucially, the conductance peaks and bulk signals scale with nanowire height, verifying the stair-stepped origin. Our results are also successfully reproduced by finite-element analysis simulations. This work establishes α-Bi4Br4 as a practical platform for high-temperature topological electronics and demonstrates a generalizable stacking strategy for designing scalable QSH systems.